The present invention is generally directed to toner compositions, and more specifically to encapsulated toner compositions. In one embodiment, the present invention is related to encapsulated toner compositions comprised of a pressure-rupturable polymeric shell, and a core containing colorants and a polymer binder with a polysiloxane-incorporated material therein. The toner shell is preferably prepared by interfacial polymerization while the core binder is preferably obtained by addition polymerization. Another specific embodiment of the present invention relates to encapsulated toner compositions comprised of a core containing certain polysiloxane-incorporated polymer binders, and dye or pigment particles, which core is encapsulated by a polymeric shell coating such as a polyurea, a polyurethane, a polyester, a polyamide, mixtures thereof, and the like, including other know suitable shells. Advantages associated with the toner compositions of the present invention include the elimination and/or the minimization of image ghosting, excellent toner fixing characteristics, superior surface release properties enabling their selection, for example, in imaging systems wherein a release fluid such as a silicone oil is avoided, substantially no blocking or agglomeration of toner particles, acceptable toner powder flow characteristics, minimal or no leaching of core components, simplicity in toner preparation, and low manufacturing cost. The toner compositions of the present invention can be selected for a variety of known reprographic imaging processes including electrophotographic and ion printing (ionography) processes. Specifically, the toner compositions of the present invention can be selected for commercial Delphax printers such as the Delphax S9000, S6000, S4500, S3000, Xerox Corporation 4060.TM., 4075.TM. and the like. They can also be utilized in electrophotographic copying and printing apparatus wherein the transfer of developed images onto paper is electrostatically accomplished, and the subsequent fixing of transferred images is accomplished by application of pressure, thermal energy or a combination of pressure and thermal energy. The toner compositions of the present invention provide excellent surface release characteristics, and the use of lubricating silicone oils or other surface release fluids to prevent image offset to, for example, the pressure roll and hot roll fuser can be avoided in most embodiments.
The toner compositions of the present invention can in one specific embodiment be prepared by first mechanically dispersing a mixture of colorants, reactive monomers, polymerization initiators, and functionalized polysiloxanes into microdroplets of specific size and size distribution in an aqueous medium containing an emulsifier or stabilizer. The reactive monomers in the resulting organic phase include one or more polyfunctional monomers for shell formation, and one or more addition-type core monomers. The polymerization initiators are typically free-radical initiators. The shell formation around the microdroplets can then be initiated by adding a second polyfunctional shell monomer which is water miscible into the reaction medium. Polycondensation occurs between the two polyfunctional shell forming monomers at the water-microdroplet interface resulting in the formation of a microcapsule shell around a microdroplet. Thereafter, the formation of the core binder polymer from the core monomer within the newly formed microcapsules can be initiated by thermal energy. Thus, one embodiment of the present invention is directed to a process for the simple, and economical preparation of pressure fixable encapsulated toner compositions by a method involving a shell-forming interfacial polycondensation and an in situ core binder synthesis by free-radical polymerization wherein there are selected at least two polymerizable core precursors one of which is a suitably functionalized polysiloxane polymer, preferably an acryloxy-functionalized, a methacryloxy-functionalized, other vinyl-functionalized polysiloxane polymer, and the like. Other process embodiments of the present invention relate to, for example, interfacial/free-radical polymerization processes for obtaining encapsulated colored toner compositions. Further, in another process aspect of the present invention, the encapsulated toners can be prepared without or with a minimum amount of organic solvents, thus eliminating or minimizing explosion hazards associated therewith; and furthermore, the solvent-free processes of the present invention therefore do not require expensive and hazardous solvent separation and recovery steps. Moreover, with the aforementioned process of the present invention there are obtained improved throughput yields of toner product per unit volume of reactor size since, for example, the extraneous solvent component can be replaced by usable liquid core monomer(s). The aforementioned toners prepared in accordance with the process of the present invention can be selected, for example, as indicated herein for permitting the development of images in reprographic systems, inclusive of electrophotographic and ionographic imaging processes wherein pressure fixing is selected. Further, the encapsulated toners of the present invention are suitable for use either in known two-component development process wherein the toners are utilized together with carrier particles, or in single-component development process wherein only the toner materials are involved.
In ion printing processes, such as the commercially used Delphax ionographic printing processes, electrostatic images are generated on a dielectric receiver surface with an ion depositing head; the images are then developed with a conductive magnetic toner, and thereafter simultaneously transferred and fixed in one single step (referred to as transfix) onto a substrate such as paper with an applied pressure. The transfix pressure can range from very low, that is for example from less than 1,000 psi to as high as 6,000 psi, provided the printing objectives are achieved and that no objectionable physical damages to the paper substrate result. One of the common problems encountered with the print quality of ionography is image ghosting. This print drawback refers to the unwarranted repetitious printing of images on paper, and arises primarily from the contamination of the dielectric receiver surface by some of the toner material. Other disadvantages associated with the use of known conventional toners usually include poor image resolution primarily because of large toner particle size, low image fix, low image smear resistance, the requirement of high transfix pressure which leads to paper calendering, high image gloss characteristics and poor image background.
Encapsulated and pressure fixable toner compositions are known. Pressure fixable toners have a number of advantages in comparison to toners that are fused by heat, primarily relating to the utilization of less energy since the toner compositions used can be fixed without the application of heat. Nevertheless, many of the prior art pressure fixable toner compositions suffer from a number of deficiencies. For example, these toner compositions generally have low fixing characteristics and must usually be fixed under an extremely high pressure, which causes the undesirable paper calendering and high image gloss characteristics. Low image resolution can also result. Further, with some of the prior art pressure fixable toner compositions, substantial image smearing can result from the high pressures used. The images generated by the prior art toners often can be readily rubbed off with pressure or removed by folding. The involvement of large quantity of solvents in the prior art processes also renders the product yield per unit volume of reactor size low; and further, the separation and recovery of solvents is usually a very costly endeavor. More importantly, with many of the prior art processes, toner particles of narrow size distribution cannot be easily achieved by conventional bulk homogenization techniques because of the high viscosity of the organic phase as contrasted with the process of the present invention where toners of narrow particle size distribution can be obtained. In addition, many prior art processes provide deleterious effects on toner particle morphology and bulk density as a result of the removal of solvent and the subsequent collapse of toner particles during particle isolation resulting in a toner of very low bulk density, which disadvantages are substantially eliminated with the process of the present invention. More specifically, thus with the encapsulated toners of the present invention control of the toner physical properties of both the core and shell materials can be readily achieved. Specifically, with the encapsulated toners of the present invention undesirable leaching or loss of core components is avoided or minimized, and image ghosting is eliminated in many instances primarily because of the presence of the polysiloxane-incorporated core binder resin component, which binder structure may also have incorporated therein a low crosslink density through the stoichiometry and functionality of the polysiloxane polymer utilized. In addition, the encapsulated toners of the present invention possess excellent powder flow properties, and do not aggregate, agglomerate or block in storage or when used in copying or printing machines. For printing in an ionographic printer such as the commercial Delphax S3000S4500, S6000 or S9000 printer, the encapsulated toner compositions of the present invention enable the generation of high fix quality prints without image ghosting. For xerographic copying or printing where the image transfer and fixing are generally two separate processes, the toner compositions of the present invention facilitate ready image transfer from photoreceptor to paper, and enables cold pressure fixability without the problem of image offset onto the pressure roller surface, often without having to use surface release lubricating fluids such as silicone oils. The encapsulated toner compositions of the present invention also enable pressure fixability with significantly lower pressures thus the common problems of paper calendering or undesirable glossy images related to pressure fixing are substantially suppressed or eliminated.
There were reported in a patentabilty search letter the following prior art U.S. Pat. No. 4,770,968, which discloses styrene butadiene terpolymers of the formula as illustrated in the Abstract, which polymers can be selected as toner resins, reference column 4, however, this patent does not disclose encapsulated toners; U.S. Pat. No. 4,814,253 discloses an encapsulated toner comprised of domains containing a polymer component having dispersed therein a release composition and thereover a host resin component comprised of toner resin particles and pigment particles, see for example columns 1 and 2, and working Example 1, column 7; U.S. Pat. No. 4,740,443 discloses an encapsulated toner which is comprised of a core containing a colorant and soft solid material, inorganic fine particles attached to the vicinity of the surface and a shell coating wherein inorganic fine particles reinforce the encapsulated toner with a thin shell, see the Abstract of the Disclosure, and also note columns 4, 5 and 6; U.S. Pat. No. 4,642,281 directed to encapsulated toner compositions which may include as additional core materials polymers including polyolefins such as silicon resins, see column 11; U.S. Pat. Nos. 3,965,022 and 4,142,982.
With further specific reference to the prior art, there are illustrated in U.S. Pat. No. 4,307,169, the disclosure of which is totally incorporated herein by reference, encapsulated electrostatic marking particles containing a pressure fixable core, and an encapsulating substance comprised of a pressure rupturable shell, wherein the shell is formed by an interfacial polymerization. One shell prepared in accordance with the teachings of this patent is a polyamide obtained by interfacial polymerization. Furthermore, there are disclosed in U.S. Pat. No. 4,407,922 pressure sensitive toner compositions comprised of a blend of two immiscible polymers selected from the group consisting of certain polymers as a hard component, and polyoctyldecylvinylether-co-maleic anhydride as a soft component. Interfacial polymerization process can be selected for the preparation of the toners of this patent. Also, there are disclosed in the prior art encapsulated toner compositions containing costly pigments and dyes, reference for example the color photocapsule toners of U.S. Pat. Nos. 4,399,209; 4,482,624; 4,483,912 and 4,397,483. In U.S. Pat. No. 4,803,144, there are disclosed microcapsule toners obtained by interfacial polymerization microencapsulation process wherein a preformed polymer is employed as the core binder. The process of this invention also illustrates the use of a suitable low boiling solvent to dissolve the polymer binder, and to promote the interfacial polymerization process.
Moreover, illustrated in a U.S. Pat. No. 4,758,506, the disclosure of which is totally incorporated herein by reference, are single component cold pressure fixable toner compositions, wherein the shell selected can be prepared by an interfacial polymerization process. A similar teaching is present in copending application U.S. Ser. No. 718,676, (now abandoned) the disclosure of which is totally incorporated herein by reference. In the aforementioned application, the core can be comprised of magnetite and a polyisobutylene of a specific molecular weight encapsulated in a polymeric shell material generated by an interfacial polymerization process.
Liquid developer compositions are also known, reference for example U.S. Pat. No. 3,806,354, the disclosure of which is totally incorporated herein by reference. This patent illustrates liquid inks comprised of one or more liquid vehicles, colorants such as pigments, and dyes, dispersants, and viscosity control additives. Examples of vehicles disclosed in the aforementioned patent are mineral oils, mineral spirits, and kerosene; while examples of colorants include carbon black, oil red, and oil blue. Dispersants described in this patent include materials such as polyvinyl pyrrolidone. Additionally, there is described in U.S. Pat. No. 4,476,210, the disclosure of which is totally incorporated herein by reference, liquid developers containing an insulating liquid dispersion medium with marking particles therein, which particles are comprised of a thermoplastic resin core substantially insoluble in the dispersion, an amphipathic block or graft copolymeric stabilizer irreversibly chemically or physically anchored to the thermoplastic resin core, and a colored dye imbibed in the thermoplastic resin core. The history and evolution of liquid developers is provided in the '210 patent, reference columns 1 and 2 thereof.
Free-radical polymerization is well known art, and can be executed in bulk, solution, or suspension polymerization. Both bulk and solution free-radical polymerization are commonly employed as in situ processes for the generation of core binder materials from the corresponding monomers within the toner microcapsules. With solution polymerization, core monomer is dissolved in a suitable solvent such as methylene chloride, while in bulk polymerization, only core monomer is employed, and the polymerization is effected in the absence of solvent.
Accordingly, there is a need for encapsulated toner compositions with the advantages illustrated herein. More specifically, there is a need for encapsulated toners wherein image ghosting is eliminated or minimized. Also, there is a need for encapsulated toners wherein images with excellent resolution and superior fix are obtained. Moreover, there is a need for encapsulated toners, including colored toners wherein ghosting, toner offsetting, undesirable leaching of core components and the like are avoided or minimized. Additionally, there is a need for encapsulated toners, including colored toners with excellent release characteristics enabling their selection in imaging systems with no silicone oils and the costly apparatus associated therewith. Furthermore, there is a need for encapsulated toners, including colored toners with substantially no toner agglomeration, aggregation or blocking, and/or long shelf life exceeding, for example, one to two years. Also, there is a need for encapsulated toners with treated surfaces to provide desirable conductivity characteristics suitable for inductive single component development. The aforementioned inductive development processes have the advantages of low development voltage, and very sharp developability which ensures high quality printing with no undesirable image background. Further, there is a need for encapsulated toners wherein surface additives such as metal salts or metal salts of fatty acids and the like can be utilized to assist in the surface release of toner during the fixing or fusing process. Another need resides in the provision of an encapsulated toner composition which can be pressure-fixed at pressures of, for example, 2,000 psi in many embodiments, which pressures are significantly lower than the 4,000 psi that are normally operating in many commercial machines such as the Delphax S6000 and S3000 printers. A further need resides in simple, economical preparative processes for the encapsulated toners. Specifically, there is a need for interfacial/free-radical polymerization processes for black and colored encapsulated toner compositions, wherein the core contains a polysiloxane-incorporated core resin binder comprised of an addition-type monomer or monomers, and a functionalized polysiloxane polymer capable of undergoing free-radical polymerization, a free-radical initiator together with colorants and other materials, and wherein solvents are eliminated in some embodiments. Furthermore, there is a need for improved processes that will enable preparation of pressure fixable encapsulated toner compositions with hard shells and soft cores, whose properties such as molecular weight, molecular weight dispersity and degree of crosslinking can be independently and desirably controlled. Moreover, there is a need for enhanced flexibility in the design and selection of materials comprising the core and shell of encapsulated toner particles, and the control of the toner physical properties, such as bulk density, particle size, and size dispersity of toner. With free-radical core polymerizations, for example, control of bulk physical properties of core binder such as melt viscosity can be obtained, for example, by the selection of appropriate monomer(s), and initiators, and concentrations as well as by the control of reaction temperature profile.